242 
PALEONTOLOGY OF NEW YORK. 
(3) 1879. 
(1) 1882. 
(1) 1882. 
(3) 1883. 
(4) 1884. 
(1) 1887. 
(3) 1887. 
(1) 1889. 
(3) 1889. 
(!) 1892. 
(4) 1892. 
Pentamerus, Barbandb. Systeme Silurien, vol. v, pis. xx, xxi, xxiii, Ixxvii, Ixxviii, Ixix, 
cxvi, cxvii, cxviii, cxix. 
Pentamerus, Hall. Eleventh Ann. Kept. State Geologist Indiana, p. 299, pi. xxvii, fig. 15. 
Pentamerus, Whitfield. Geology of Wisconsin, vol. iv, p. 291, pi. xvii, figs. 11-13. 
Pentamerus, Davidson. Bi-itish Silurian Brachiopoda, Suppl., p. 164, pi. ix, figs. 25, a. 
Qyindula, Walcott. Monogr. U. S. Geol. Survey, vol. viii, p. 159-161, pi. iii, figs. 4, 7; 
pi. xiv, fig. 15 ; pi. XV, fig. 5. 
Antirliynclionella, CEiilert. Fischer’s Manuel de Conchyliologie, p. 1311. 
Sieherella, QHiilert. Fischer’s Manuel de Conchyliologie, p. 1311. 
Pentamet'us, Nettelroth. Kentucky Fossil Shells, p. 64, pi. xxiii, figs. 12-14. 
Pentamerus, Nettelroth. Kentucky Fossil Shells, pp. 59, 63, pi. xxvii, figs. 25-27; 
pi. xxxiii, figs. 25-29, 31-33. 
Pentamerus, R. Etheridge, Jr. Pentameridie of New South Wales; Records Geol. Survey 
N. S. W., vol. iii, pt. 3, p. 52, pi. xi, figs. 5-9. 
Pentamerus, Whiteavbs. Contributions to Canadian Palaeontology, vol. i, p. 290. 
The elongate, subequally biconvex pentameroids being restricted to the 
divisions above discussed, there remains to be considered the large group of 
galeatiform shells which are characterized by their usually small size, inequal 
convexity, and deep, overarching pedicle-valve. A typical representative of 
this variable and undoubtedly heterogeneous group is the well-known 
Atrypa {Pentamerus) galeata, Dalman. These are the fossils embraced in 
DE Verneuil’s grouping as “Pentamerus avec sinus,” all having a median sinus 
more or less strongly developed. Two divisions of the first order maybe based 
upon the position of this sinus, namely, those having it (1) on the pedicle-valve, 
and (2) on the brachial valve. In the former division belong such species as 
P. fornicatus, Hall, and P. Areyi, sp. nov., of the Clinton group; P. linguifer, Sow- 
erby, and P. ventricosus, Hall, of the later Silurian, as well as shells which have 
been referred to the Devonian subgenus, Pentamerella (P. arata, Conrad, P. duhia. 
Hall, etc.). With the latter division we may place P. galeatus, Dalman, P. nuc¬ 
leus, P. pseudogaleatus, Hall, P. {Sieherella) Sieberi, von Buch, etc., of the Silurian, 
and the various species of the subgenus Gypidula {G. comis, Owen, G. Itzviuscula, 
Hall, G. Romingeri, sp. nov.). This grouping might form a very convenient 
arrangement of these species, were the field clear of generic terms, but in each 
group designations of unequal value have been introduced, based upon varia¬ 
tions in other respects than contour alone. The Devonian members of each 
group develop with more or less distinctness a striated cardinal area and small 
and convex deltidial plates, with some accompanying variation in the character 
